1. Field of Invention
The present disclosure of invention relates to an interpolation device that is usable in a display apparatus such as one that charges image pixels to desired voltage levels. More particularly, the present disclosure relates to an interpolation device capable of providing accurate interpolation for serial image signals having values for which corrections are not directly defined by a lookup table.
2. Description of Related Art
Generally, liquid crystal displays provide a desired voltage between two electrodes of a given pixel unit in order to apply an electric field to a liquid crystal material layer of the unit, where the desired voltage defines an intensity of an electric field to thereby control the transmittance of light passing through the liquid crystal material layer, thereby obtaining a desired image intensity from the given pixel unit. In order to prevent the image from being deteriorated by a unidirectional electric field applied to the liquid crystal layer for a long time, a reversal drive method is often employed with liquid crystal displays to periodically reverse a polarity of data voltage with respect to a common voltage. Such polarity reversal may occur on a frame-by-frame basis or longer, on a column basis, a row basis, or a dot-by-dot basis. Irrespective of how often polarity reversal occurs, when imagery changes from frame to frame, voltage across the electrodes of the pixel unit has to be driven from a first level to a different second level.
Recently, liquid crystal displays have adopted a dynamic capacitance charging compensation (DCCC) scheme to improve the response speed at which liquid crystals change state. According to the DCCC scheme, a modified data voltage is applied for a present frame in place of an original data voltage (hereinafter, also referred to as “present data voltage”) where the modified data voltage includes a compensation for the difference between the desired present data voltage to be formed across the pixel capacitance and a data voltage remaining on the capacitance from a previous frame (hereinafter, referred to as “previous data voltage”). This compensation helps to increase the speed at which the liquid crystal capacitor is charged to the desired present data voltage.
In terms of more detail, if an absolute value of potential difference between the previous data voltage and the desired present data voltage is greater than a preset reference value, the liquid crystal display adopting the DCCC scheme has applied to it a drive voltage greater than the desired present data voltage so as to thereby increase the charge speed of the equivalent RC circuit (resistor-capacitor circuit) associated with the liquid crystal capacitor.
In one class of embodiments, a lookup table (LUT) is used to determine the magnitude of the charge-hurrying drive voltage. In order to limit the amount of storage memory space needed by the LUT and according to one approach, only the more significant bits (MSB's) of the pixel data are used. An imprecise (linear and symmetrical) interpolation equation is used for dealing with small differences of gray scale. Since such an imprecise interpolation equation may fail to provide correct drive voltages in cases where there are moderate differences of gray scales between the previous data voltage and the desired present data voltage rather than very large differences or essentially no differences, the display system can fail to display subtle changes of gray scale across an image, thereby depriving viewers of the image resolution intended by the original data.